Toobin—who has been harshly critical of Greenwald and NSA leaker Edward Snowden—appeared on Anderson Cooper's show just after Miranda himself, along with Greenwald, spoke about his experience.

Miranda said he didn't know what was on the files that were confiscated. "I was just taking materials back to Glenn," he said.

Greenwald declined to say what Miranda was carrying, but added, "Every single newsroom in the United States...has classified information...so if you want to support the idea that states can just go and confiscate from journalists classified information, you should be demanding that your government go physically into newsrooms and seize whatever classified information is there."

Asked if he thought the British were right to detain Miranda, Toobin said, "I sure do."

"I don't want to be unkind, but he was a mule," he said. "He was given something, he didn't know what it was, from one person to pass to another at the other end of an airport. Our prisons are full of drug mules."

"They knew who he was, they knew he wasn't connected to some terrorist group," Cooper pointed out.

"If terrorists know how we surveil their cell phone call, how we surveil their texts, that could be useful to terrorists," Toobin said.

"But couldn't any information published by journalists be used by journalists in some way, and can't that excuse be used to detain journalists?" Cooper asked.

"It would have to be classified information of this kind," Toobin said. He later added that "the word journalism is not magical immunity sauce that you can put on anything and eliminate any sort of liability."

Jesselyn Radack, a former whistleblower who works for the Government Accountability Project, defended Miranda against Toobin's assertions, calling them "vacuous."

"No matter what was on [Miranda's files], it obviously had to do with journalism," she said. "David was serving as an in-between, not as a drug mule."

"If the British government thought there were stolen documents that were being transported, why don't they have the right to stop this person and check?" Cooper asked.

"The British government, if it thought they had stolen documents, could go through the criminal process rather than using an anti-terrorism law," Radack said.

"He wasn't sent to the gulag," Toobin said.

"I hope the next time Mr. Toobin is stopped for nine hours and detained with no due process on an anti-terrorism law that he is equally as generous with his assessment," Radack replied.

Greenwald responded to Toobin's comments on Twitter:

Most amazing feat of US Govt is to get journalists to take the lead in demanding the criminalization of journalism http://t.co/sDvbVHYfnk

Reporter Kevin Gosztola also took aim at Toobin, by quoting from a book by author Michael Isikoff which said that Toobin had "absconded with large loads of classified and grand-jury related documents from the office of Iran-Contra independent counsel Lawrence Walsh" in the late 1980s.

UPDATE: In an interview with The Huffington Post, Toobin called Gosztola's blog post "completely wrong." He said that, upon leaving his post at the Office of Independent Counsel, he had presented every document he intended to take with him to his superiors, and had received approval. He added that, when he wrote a book about his time in government, the CIA had reviewed it and had not made him change it.

"I didn't steal any information," he said. "I played by the rules. I followed the law."

He also said that anyone surprised by his enthusiastic defense of the NSA against Snowden had misjudged him.

"I am not an advocate of a party line, I hope, on any issue," he said. "I'm not a liberal pundit. I'm not a conservative pundit. I'm a journalist."

LONG ISLAND, NY - CIRCA 1969: Socialite and heiress Gloria Vanderbilt poses for a portrait session with her sons Anderson Cooper (left) and Carter Vanderbilt Cooper in their home in circa 1969 in Southampton, Long Island, New York. (Photo by Jack Robinson/Hulton Archive/Getty Images)